Version 5.0 The LEDA User Manual

9.13 Checksummers ( checksummer base )
1. Definition
The class checksummer base is the base class for all LEDA checksummers. It cannot be
instantiated. In order to avoid repeating this documentation for each derived class below
we will discuss its members here.
When a checksummer is used in encoding mode it can add checksums to the output stream.
This is controlled by the checksums in stream flag. If this flag is set and the block size is
zero (default setting) then one checksum is appended at the end of the stream. If the flag
is switched on and the block size b is positive then a checksum is written for every block
of b characters.
When the checksummer is used in decoding mode this flag specifies whether the source
stream contains checksums. If so, they will be compared against the computed checksum
for the stream (or for the respective block if the block size is positive).
If you use a checksummer in a coder pipe (cf. Section 9.23) then it should be the first
coder in the pipe. This ensures that the checksum is computed for the original input.
Finally, we want to point out that all checksummers provide fast seek operations (cf. Section
9.22).
#include < LEDA/coding/checksum.h >
2. Creation
checksummer base C(streambuf ∗ src stream = 0, streambuf ∗ tgt stream = 0,
bool own streams = false);
creates an instance C which uses the given source and target
streams. If own streams is set, then C is responsible for the destruction
of the streams, otherwise the pointers src stream and tgt stream
must be valid during the life-time of C.
checksummer base C(const char ∗ src file name, const char ∗ tgt file name = 0);
creates an instance C which uses file-streams for input and output.
3. Operations
Standard Operations
void C.encode( ) encodes the source stream and writes the output to
the target stream.
void C.decode( ) decodes the source stream and writes the output to
the target stream.